N Value, SPT Value

The number of blows required to drive a 2 in. O.D., 1 3/8 in. I.D, 24 in. long, split soil sampling spoon one foot with a 140 lb. weight freely falling 30 in. The count is recorded for each of three 6 in. increments. The sum of the second and third increments are taken as the N Value in blows per foot. (See ASTM D1586 - The Standard Penetration Test.)

Necking

Reduction in area of cast-in-place concrete in a pile, either uncased or thin cased due to soil pressure or improper method of installation.

Needle Beam

A structural beam inserted through a hole in a wall to support the wall during underpinning, jacking or excavating operations beneath it. The beam transfers the wall load to a temporary or a newly installed foundation.

Needle Gauge

A pressure guage with a needle stem for measuring air or steam pressure in pressure hose, by puncturing the wall of the hose with the needle stem.

Needle Gun

A hand held tool with a group of wired or needles in the end that vibrate when on and is used to clean a weld by beating the slag or covering from the welded area.

Needle Piles

Very small diameter slender driven steel tubular or rail section piles used in underpinning operations.

Negative Batter

See Aft Batter.

Negative Skin Friction

1. Side frictiona long a pile surface directed downward.
2. Effect of settling soil that grips a pile by friction and adds a downward weight to the structure load. Also called Downdrag.

Net Settlement

See Settlement, Net.

Non-Displacement Piles

Piles formed by boring or other methods of excavation. H, open-end pipe and sheet piles are considered low-displacement piles.

Observation Well

A perforated pipe installed in the ground for monitoring groundwater level.

Offshore Lead

A pile hammer lead which has an upper section wherein the hammer is contained and a lower section which closely fits about and guides the pile. The hammer is supported and aligned by the pile after engagement. The pile is usually supported by a template. Also called Cage, Can Lead, Chuch Lead, Rope, Suspended Lead, Pipe Lead.

Oil Reservoir

A part in single-acting hammers which over the valve and holds oil to lubricate the valve. The same as the valve cover in double-acting mechanical-valve hammers.

Oiler

1. A device for injecting oil in air or steam lines; also called Lubricator.
2. Assistant equipment operator.

On Grade

Placed directly on the ground, or leveled or excavated to the proper elevation.

Orange Peel Dredge

A dredge with a bucket or auger that looks like an unbroken orange peel curled up.

Order Lengths

Lengths of pile expected for the project, ordered by either the owner, the A/E or contractor from the supplier.

Oslo Point

A 3 to 5 in. shaft of hard steel is set into the lower end of an H-pile by slitting the shaft or cutting the web of the pile for some distance, and then welding the shaft to the H-pile. Utilized to secure a toe hold in sloping rock. Can also be fitted to end plate of a pipe pile.

Overdriving

1. Driving that exceeds the maximum warranted hammer blow count or damages the material comprising the pile.
2. Hitting the pile more than the optimum or required number of blows per increment of advance.
3. Continuing to drive after penetration of the pile is stopped.

Overhead Leads

See Leads, Extended.